An activatable NIR fluorescent rosol for selectively imaging nitroreductase activity

Journal article

Hypoxia (pO2 ≤ ~1.5%) is an important characteristic of tumor microenvironments that directly correlates with resistance against first-line therapies and tumor proliferation/infiltration. The ability to accurately identify hypoxic tumor cells/tissue could afford tailored therapeutic regimens for personalized treatment, development of more-effective therapies, and discerning the mechanisms underlying disease progression. Fluorogenic constructs identifying aforesaid cells/tissue operate by targeting the bioreductive activity of primarily nitroreductases (NTRs), but collectively present photophysical and/or physicochemical shortcomings that could limit effectiveness. To overcome these limitations, we present the rational design, development, and evaluation of the first activatable ultracompact xanthene core-based molecular probe (NO 2 -Rosol) for selectively imaging NTR activity that affords an "OFF-ON" near-infrared (NIR) fluorescence response (> 700 nm) alongside a remarkable Stokes shift (> 150 nm) via NTR activity-facilitated modulation to its energetics whose resultant interplay discontinues an intramolecular d-PET fluorescence-quenching mechanism transpiring between directly-linked electronically-uncoupled π-systems comprising its components. DFT calculations guided selection of a suitable fluorogenic scaffold and nitroaromatic moiety candidate that when adjoined could (i) afford such photophysical response upon bioreduction by upregulated NTR activity in hypoxic tumor cells/tissue and (ii) employ a retention mechanism strategy that capitalizes on an inherent physical property of the NIR fluorogenic scaffold for achieving signal amplification. NO 2 -Rosol demonstrated 705 nm NIR fluorescence emission and 157 nm Stokes shift, selectivity for NTR over relevant bioanalytes, and a 28-/12-fold fluorescence enhancement in solution and between cells cultured under different oxic conditions, respectively. In establishing feasibility for NO 2 -Rosol to provide favorable contrast levels in solutio/vitro, we anticipate NO 2 -Rosol doing so in preclinical studies.

Authors: Klockow, JL; Hettie, KS; LaGory, EL; Moon, EJ; Giaccia, AJ

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Elsevier
• Journal: Sensors and Actuators B: Chemical
• Volume: 306
• Article number: 127446
• Publication date: 2019-11-30
• Acceptance date: 2019-11-19
• DOI: 10.1016/j.snb.2019.127446
• EISSN: 0925-4005
• ISSN: 0925-4005
• Pmid: 32265579
• Language: English
• Keywords: FFR; nitroreductase; hypoxia; near-infrared; activatable probe; imaging; fluorescence